Step 1 : Stop all the daemons, Add the user to sudo file for all the nodes.
Please make the following change as given below.
1) Login as root
su
2) Enter the given command to edit sudoers file:
visudo
3) Change the following as per screen-shot and to save the change press Esc >> Shift:wq
Step 2 : Format the namenode
hadoop namenode -format
Step 3 : Delete data directory mentioned in hdfs-site.xml
rm -rf directory_path
Step 4 : Again re-create the data directory and give chmod 755 permission to all the data directory
mkdir directory_path
chmod 755 directory_path
Please let me know if you have any further issue regarding this.